Sets matrix to a specified size (zero is OK as long as both r and c are zero).

The value of the new data depends on resize_type: -if kSetZero, the new data will be zero -if kUndefined, the new data will be undefined -if kCopyData, the new data will be the same as the old data in any shared positions, and zero elsewhere.

You can set stride_type to kStrideEqualNumCols to force the stride to equal the number of columns; by default it is set so that the stride in bytes is a multiple of 16.